The present disclosure relates to methods and apparatuses that are useful in an imaging apparatus for producing printed copies. In particular, the methods and apparatuses relate to using a tunable metamaterial for modulating a light beam during the imaging process.
A typical flexible electrophotographic imaging member belt comprises at least one photoconductive layer. The imaging member is imaged by uniformly depositing an electrostatic charge on the imaging surface of the electrophotographic imaging member and then exposing the imaging member to a pattern of activating electromagnetic radiation, such as light, which selectively dissipates the charge in the illuminated areas of the imaging member to create an electrostatic latent image in the non-illuminated areas. Put another way, a light beam, such as from a laser or a light-emitting diode, is used to selectively dissipate charges in specific locations on the imaging member. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking toner particles on the imaging member surface. The resulting visible image can then be transferred to a suitable receiving member or substrate, such as paper.
To create the light pattern that is applied to the surface of the imaging member, the light beam must be switched on and off at an extremely high speed. Because switching the light source (typically a laser) on and off may not be practical or economical, a modulator is used. Generally speaking, the modulator is used to interrupt the light beam as it travels from a light source to the imaging member.
Specific modulators include Pockels cells and Kerr cells. Pockels cells and Kerr cells take advantage of changes in the refractive index of a material in response to an applied electric field. Generally speaking, when combined with polarizers, light will be transmitted through these cells when an electric field is applied, and will not be transmitted when the electric field is turned off.
Pockels cells require manual adjustment and complex driver electronics for operation. In addition, if the crystal axis and ray axis are not aligned, a large phase shift and thus modulation errors occur. Kerr cells generally contain nitrobenzene, which is recognized as a highly toxic, hazardous material that is readily absorbed through human skin.
In addition, both Pockels cells and Kerr cells require either a high voltage (thousands of volts) or high amperage (tens of amperes) external electric field. Both types of cells also exhibit limited frequency response.
It would be desirable to develop modulation devices and methods that overcome the deficiencies of Pockels cells and Kerr cells for use with imaging apparatuses.